The present disclosure relates to a structure and a method for filling via holes formed in a multilayer printed circuit board, and more particularly, to a structure and a method for filling via holes formed in multilayer printed circuit boards, the structure and method enabling high-current transmission even in a narrow space in such a way that a via hole formed when a general typical multilayer printed circuit board is manufactured is first filled with Cu and Ag plating, and the remaining vacant space is completely filled with a solder cream, thereby increasing the amount of conductors.
Printed circuit boards (PCBs) express the electrical wiring for connecting circuit components in wiring shapes on the basis of circuit design and reproduce electrical conductors on an insulator through a method suitable for the design. Various electronic components are mounted on such a printed circuit board, and wiring is formed such that the components are electrically connected.
Recently, along with the development of electronic devices, PCBs have been made to have a high-density or a multilayer. In such a manufacturing method of high-density/multilayered PCBs, a configuration for electrical connection and smooth current flow between the patterns formed in each layer is required.
According to a manufacturing process of multilayer PCBs, firstly, a printed circuit board having a copper foil formed on the entire surface thereof is prepared.
Next, a photosensitive resin film is printed on the surface of the copper foil layer using a wiring-patterned film. Using the characteristics of the photosensitive resin, a circuit forming step in which a wiring pattern is formed by etching a desired pattern on the copper foil layer is performed. After forming a circuit, a step in which the printed circuit board is heated and pressed by using a press to thereby successively laminate pattern layers and insulating layers is performed. Recently, a manufacturing method using lamination through a build-up method in which layers are laminated one-by-one has been widely used.
After the laminating step, a via hole processing step for electrical connection between the pattern layers is performed. When the via hole processing is completed, a plating process step for electrically connecting a plurality of laminated layers is required.
Through the plating process, the processed via holes are filled with metal, and the electrical connection between the pattern layers is thereby obtained. After the plating process step, printing a solder resist and printing letters are performed. The printing of a solder resist is used to minimally suppress the exposure of copper. In this step, although the portion connected to electronic components is not covered but exposed, non-required portions such as wiring portions are covered with a solder resist to prevent copper from being oxidized by air or peeled off by external shock, or to prevent a short-circuit. In the printing of letters, names of components to be mounted or names of constituent parts are printed.
Subsequently, the multilayer printed circuit board is manufactured through steps including an outer shape processing step for processing the outer shape of the printed circuit board so as to match the shapes of products and devices which are finally mounted, an appearance inspection step, an electrical inspection step, a film development step for producing a film for printing a wiring pattern or a solder resist, and the like.
In manufacturing the multilayer printed circuit board, the electrical connection of the circuit patterns between each layer built up through lamination is performed by mainly using a method in which the inner walls of via holes are made conductive through plating. Accordingly, in a manufacturing process of the multilayer printed circuit boards, a large number of via holes are formed to electrically connect each layer and ach circuit pattern with each other. Circuit patterns between the plurality of layers, which serve as upper or lower layers, are electrically connected through via holes filled with plating.
Typical via hole filling methods for electrically connecting circuit patterns include a first typical art in which via holes are made conductive in a hole shape, and then, the insides of the via holes are filled with insulating resins or conductive pastes. Also included is a second typical art in which a chemical plating layers and an electrical plating layers are formed on the side walls of the via holes, and then, the insides of the via holes are filled with a photosensitive ink. Further included is a third typical technique which is most widely used at present as the conductor patterns gradually become fine, and in which the insides the via holes are filled by using electrical copper plating.